Cerebrovascular disorders such as cerebral infarction occupy the top ranks in terms of cause of death. If the discovery timing of treatment is delayed, sometimes serious sequelae remain. Therefore, early discovery of cerebrovascular disorders and diagnosis of the degree of seriousness are extremely important.
The nuclear medicine image diagnostic techniques such as SPECT, MRI, CT, and etc. are known as a main diagnostic technique for cerebrovascular disorders. The nuclear medicine image diagnostic techniques make finding the amount of cerebral blood flow at the tissue level relatively easily. That is why these techniques are widely used in the early diagnosis of cerebrovascular disorders and diagnosis for the degree of seriousness.
The Microsphere method and IMP-ARG method are mainly used as diagnosing cerebrovascular disorders using the nuclear medicine image diagnostic technique. In the Microsphere method, a cerebral blood flow-preparation product at an early stage following administration is regarded as a Microsphere and the local cerebral blood flow is obtained from nuclear medicine image data based on a one-compartment model. The advantages of this method are its straightforward theory and easy calculation; however, there are disadvantages such as its highly invasive properties due to the necessity of continuous blood sampling of arterial blood. Furthermore, because the move of drugs from tissues into the blood vessels is not taken into consideration, the determining accuracy in the later stages after the drug is administered deteriorates, creating a further disadvantage in that the point of data collection time is limited to the relatively early stages after having been administered.
Instead of the continuous blood sampling of arterial blood, the NIMS method has been proposed in which an input function is estimated using a time activity curve based on dynamic planar data of the chest part; however, this method is also based on the one-compartment model, preventing sufficient determining accuracy from being obtained at the later stages after the drug is administered.
On the other hand, the IMP-ARG method is a method for obtaining cerebral blood flow according to the Look-up table approach by administering IMP (N-Isopropyl-4-[123I]Iodoamphetamine hydrochloride) as a radioisotope medicine and substituting a count after a certain time has elapsed in a formula of a two-compartment model in the nuclear medicine brain imaging (Non-patent Document 1). With the IMP-ARG method, a method for correcting the standard input function may be used by obtaining blood sample data of an artery at one point, providing an advantage of being less invasive than the Microsphere method for which continuous blood sampling data is required.
[Non-patent Document 1]
Hidehiro Iida et al, “Quantative Mapping of Regional; Cerebral Blood Flow Using Iodine-123-IMP and SPECT”, The Journal of Nuclear Medicine, December 1994, Vol. 35, No. 12, pp 2019-2030
[Non-patent Document 2]
Kyeong Min Kim et al., “Quantitative Mapping of basal and vasareactive cerebral blood flow using split-dose 123I-iodoamphetamine and single photon emission computed tomography.”, NeuroImage, 2006, Vol. 33, pp 1126-1135
[Non-patent Document 3]
Kazuo Hashikawa et al., “Split Dose Iodine-123-IMP SPECT: Sequential Quantitative Regional Cerebral Blood Flow Change with Pharmacological Intervention.”, Journal of Nuclear Medicine, July 1994, Vol. 35, No. 7, pp 1226-1233
[Non-patent Document 4]
Yoshifumi Kawamura “A method for estimating radiation remaining in the brain using static-SPECT after the first time when 123I-IMP is administered in a two occasion-study on the ARG method cerebral blood flow increase rate and the SPECT count increase rate-” Nuclear Medicine, 2002, Vol. 39. pp 125-134
With the IMP-ARG method, sometimes changes in sought values due to the injection of a drug with vasodilator action such as acetazolamide, etc. are measured for the purpose of evaluating the circulation reserve ability of cerebral blood vessels. In this case, SPECT measurements have to be performed in two occasions, for the case in which acetazolamide has been administered (under medication) and the case in which it has not been administered (rest state). Here, it is necessary to wait for sufficient clearance time after the finish of cerebral blood flow SPECT imaging in rest state to perform cerebral blood flow SPECT imaging under medication. However, it needs two days to perform the cerebral blood flow SPECT imaging under medication after waiting for sufficient clearance from the finish of the cerebral blood flow SPECT imaging in rest state. So it puts significant burden onto a subject as well as onto the medical institutions performing the test. With such a background, various methods of performing a SPECT test in one day both in rest state and under medication have been studied and clinically applied (Non-patent Documents 2 to 4).
As described above, the IMP-ARG method is one of the best diagnostic techniques for cerebrovascular disorders. However, even with the IMP-ARG method, blood sampling of arterial blood is required. In general, blood sampling of arterial blood is more invasive than blood sampling of venous blood. With such a background, it has been desired to realize a technique for determining the amount of cerebral blood flow by less invasive operations. But no such method had been known. Furthermore, if venous blood is mixed in when blood sampling of arterial blood is taking place, there is a problem in that the reliability of the obtained data deteriorates.
Moreover, for evaluating the circulation reserve ability of cerebral blood vessels, it is necessary to obtain count changes under medication without being influenced by the radioisotope medicine that is administered during SPECT measurement in rest state. In this case, in terms of reducing the burden on the subject and the examining institution, it is desired to perform the test within one day. Consequently, various techiniques such as the one described in the above non-patent documents have been developed. In order to fully satisfy such a need with respect to performing the test within a day, proposing a new method that has not been developed has significant values in and of itself. Furthermore, there was no technique for determining cerebral blood flow which performs both the test in the rest state and the test under medication within a day, while it does not need to sample the arterial blood.
The present invention has been designed in view of the above situation and with the purpose of providing a technique for accurately determining cerebral blood flow by less invasive means capable of performing a plurality of SPECT tests in a single day.